1. Field of the Invention
The present invention relates to a bonding apparatus capable of increasing product quality by realizing high-precision control of a pressing force applied upon mounting of an electronic component on a substrate by bonding, and to a bonding method capable of providing high-quality products stably.
2. Description of the Related Art
Electronic devices (e.g., computers) have become faster and smaller, and there is an increasing demand for high-density packaging of electronic components. Against this background, substrates for large scale integration have been used, in which a plurality of electronic components is arranged on a substrate in layers. In addition, for tighter packing of electronic components, flip-chip bonding has been employed in which bumps are formed on an electronic component that is to be mounted on a substrate, and the bumps are then pressed against the substrate and welded thereto. High pin count and device miniaturization have been realized in this approach, with an increasing demand for reduced bump diameter and reduced pitch between bump connection terminals.
However, if bump connection terminal pitch reaches as small as 40 μm or less, a concern arises regarding the occurrence of connection defects, such as short-circuits between terminals, and damages to the electric component if it fails to achieve high-precision positioning (tolerances to ±1 μm) and/or stable load control because of variations in the fabrication precision of the substrate and in the formation of bumps. Short circuits between terminals occur due to, for instance, excessively crushed bumps and displacement after recognition. Damages to the electronic component include failures of, for example, bumps and terminals of the electronic component and substrate.
The following bonding apparatus has been conventionally used for electronic component bonding: A bonding apparatus which has a bonding tool provided so as to be capable of moving up and down, and a load sensor for detecting load that has been applied to an electronic component by the bonding tool. In such a bonding apparatus the load sensor is provided on the upper side of the bonding tool support and the load sensor is allowed to contact the bonding tool support to cause both a bonding head attached with the bonding tool and load sensor to move down, bonding the electronic component to the substrate. The bonding apparatus is so configured that, at this point, load (pressing force) applied by the bonding tool is detected by the load sensor that is in contact with the bonding tool.
The followings are specific examples of conventional bonding apparatus used: A bonding apparatus in which a bonding tool support is suspended from a head unit by a spring (see Japanese Patent Application Laid-Open (JP-A) No. 2000-183114); a bonding apparatus equipped with two different load detection mechanisms: one configured to detect decreasing load, and one configured to detect increasing load, at a time when a given level of load applied to a bonding tool support has caused a bonding tool to press an electronic component (see Japanese Patent Application Laid-Open (JP-A) No. 2002-76061); a bonding apparatus configured to carry out feedback control by previously creating a given level of thrust in a cylinder (see Japanese Patent Application Laid-Open (JP-A) No. 2001-68895); and a bonding apparatus in which a bonding head is provided with a parallelism adjustment mechanism by which the parallelism of a bonding tool is determined by a parallelism detection sensor (see Japanese Patent Application Laid-Open (JP-A) No. 2001-223244).
However, when high-precision positioning and high-precision load control are required in connection with reduced pitch between bump connection terminals, variations occur in the in-plane stress due to variations in the precision of components (e.g., substrates and bumps), even though the detected load values falls within a set reference load for a bonding operation, leading to reduced product yields due to connection failures and the like.
With respect to the set reference load—a whole pressure created during a bonding operation—there arises the following problem: The bonding tool support is provided with a number of components: mechanical sections (e.g., slide guides, a shaft, a cylinder and a spring) that constitute a lifting and lowering mechanism; mechanical sections for attaching and cooling an electronic component and for adjusting the inclination of the electronic component; and a number of parts (e.g., wires and pipes) for connecting these mechanical sections together. Thus, in a case of a load sensor provided on the upper side of the bonding tool support, available locations or areas for the load sensor are limited. In addition, the load sensor is susceptible to heat generated due to friction of the components and thus tends to produce different values for the detected load. The measured pressure value only means the load applied to the bonding tool support, and includes escaping loads such as inclined loads acting on the components, and horizontal components. For this reason, the measured load value is not necessarily equal to the value for load acting on the bonding portions, thus requiring periodical load calibration.
Accordingly, bonding apparatuses with conventional load detection mechanisms, as disclosed in the foregoing Patent Literatures, cannot achieve further increase in the product quality; therefore, bonding technology has been sought after that enables high-precision pressing force control for increased product quality.
It is an object of the present invention to solve the foregoing conventional problems and to achieve the object described below.
Specifically, it is an object of the present invention to provide a bonding apparatus capable of increasing product quality by realizing high-precision control of a pressing force applied upon mounting of an electronic component on a substrate by bonding, and to a bonding method capable of providing high-quality products stably.